1. Field of the Invention
The present invention relates to a power amplifier (PA), and more specifically, to a multimode PA that accommodates both saturated and linear modes, and thus is capable of adapting to a plurality of telecommunication formats. The present invention also relates to a method of switching among different operating modes with the multimode PA and a mobile terminal that uses the multimode PA. The present invention, therefore, is in the field of PA technology.
2. Description of the Prior Art
With the third generation (3G) mobile telecommunication technology deployed on a largescale, 2G and 3G standards will coexist for a long period of time. Therefore, the resources telecommunication operators invested on 2G deployment would not be wasted while the operators are phasing-in 3G smoothly so to lower the cost. Currently, three 3G standards—TD-SCDMA, CDMA2000 and WCDMA 3-co-exist in the Chinese market. In addition, Wi-Fi and WiMax, as supplementary technology of 3G-LTE, also have significant potential. Thus, the market environment in which a plurality of telecommunication standards co-exists requires more adaptability from mobile terminals.
Multimode technologies comprise the multimode adaptability of base stations and mobile terminals. With mobile terminals, the multimode adaptability cannot be realized without a multimode power amplifier (PA). In general, there are two types of PAs: PAs operating in saturation mode or in linear mode. A saturated PA is needed in the Global System for Mobile Communication (GSM) system. It adopts GMSK modulation and is capable of compressing the amplitude of its radio frequency (RF) signals as the signals do not contain modulation information. In a CDMA-based 3G system, such as EDGE, TD-SCDMA, TD-LTE or CDMA2000, a linear PA is required.
One feature of a PA in saturation mode is that within a certain range of input power, the output power is not determined by the input power but by the power supply of the PA's output stage and the load impedance. With a PA in linear mode, the output power is always proportional to the input power. Even with telecommunication standards that require a linear PA, such as EDGE, TD-SCDMA, TD-LTE, or WCDMA, the requirements on the PA's output power, gain and current may differ as the internet standard may be different. This analysis shows that a saturation PA and a linear PA requires completely different design, and the transistor parameters and operating current that meet the requirement of their respective circuits are very different.
In order to meet the requirements imposed by different telecommunication standards to a PA, the current technology usually apply several single mode PAs coupled with a gating switch. However, the method significantly increases the cost. For example, a Chinese patent application number 201110346135.X, disclosed a power amplifying module, a multimode RF transceiver, a RF front-end module, a multimode terminal module and a method of sending signals from a multimode terminal. The patent comprises two operating modes, the first is GSM-mode signals and the second is TD-SCDMA-mode signals. When the controlling signal is a low-frequency signal in the first mode, the controller sends a signal of saturation mode to the low-frequency amplifier. When the controlling signal is a high-frequency signal in the first mode, the controller sends a signal of saturation mode to the high-frequency amplifier. When the controlling signal is in the second mode, the controller sends a signal of linear mode to the high-frequency amplifier.
A Korean patent application number KR 10-2010-0051808, discloses a device and method that assembles power amplifying units in one module to support multimode mobile terminals, so to reduce the space and cost of multimode mobile terminals. The PA of mobile terminals comprises a first amplifying unit and a second amplifying unit. The first amplifying unit defines the four bands of GSM as low-frequency bands and high-frequency bands, and then amplifies signals of the low-frequency bands. The second amplifying unit amplifies signals of the high-frequency bands and TD-SCDMA signals, with both signals selected by a TD-SCDMA controlling and switching unit.
In addition, a U.S. patent application Ser. No. 09/455,813, introduces a PA comprising a carrier amplifier and a peak amplifier for multimode mobile telecommunication devices. The peak amplifier has an adjustable bias voltage, so that a regulator can adjust the voltage to a predetermined level according to the selected telecommunication mode. The bias voltage of the peak amplifier maintains the same as long as the communication mode stays the same. The modulation efficiency and linearity of a specific telecommunication mode can be optimized by adjusting bias points of the peak amplifier that are relevant to the selected telecommunication mode.